The permissable wheel loads on a paved road surface have been steadily increased over the years resulting in damage to the road such as unevenness, cracks and the like and accurate investigation and collection of data relating to such road surface conditions is now urgently desired. Among various road conditions, a groove caused by a vehicle wheel, which is called a road "rut", is especially important, and to survey the same quantitatively to take immediate proper corrective action has now become an important problem in view of traffic safety, especially for highways and main roads.
A process for surveying road ruts is known in which a profile meter of from 3 to 4 meters in length, or a ruler is placed on a road in the transverse direction thereof while traffic is stopped, and the height from a base line previously set on the profile meter to the road surface is recorded by direct reading at respective measuring points provided at intervals of 10 cms or so in the transverse direction. The rut dimension is then calculated from the results of such recording. This conventional process necessitates the suspension of traffic on the road over a distance of about several hundred meters, and hence its implementation is disadvantageous from the view point of traffic hindrance, especially for roads which have large traffic volumes both day and night.